Intralesional therapy for cancer—that is, direct injection of an anti-cancer drug into the lesion—was first
taken seriously back 1975. A story in Cancer reported on a 77-year-old patient with 64 intracutaneous metastases and a pulmonary metastatic deposit.
Over an eight-month period, he received inoculations with Bacille Calmette-Guérin (BCG) in 17 of his lesions, and each resolved. At the same time, the
pulmonary metastasis regressed more than 50 percent. The treatment was locally ablative and, at the same time, it induced host immune anti-tumor activity in
regional and distant uninjected metastases through a systemic adjuvant response.

Passion for the approach cooled after a subsequent
trial, in which researchers found anaphylactic reactions and death occurred due to disseminated BCG. When randomized trials of BCG also failed to confirm a
significant clinical benefit, intralesional therapy went out of fashion.

Directly attacking the lesions, however,
remains an obvious way to treat cancers, and in the treatment of melanoma, there are three candidate drugs currently under investigation as intralesional
agents: OncoVEXGM-CSF, now called T-VEC (Talimogene laherparepvec), Allovectin-7 and Rose Bengal (RB) disodium.

OncoVEXGM-CSF

OncoVEXGM-CSF, now called T-VEC (Talimogene
laherparepvec), is Amgen’s entry in the intralesional sweepstakes and is an investigational oncolytic immunotherapy designed to selectively replicate
in tumor tissue and to initiate a systemic anti-tumor immune response.

In early 2014, Amgen announced findings
from a pre-specified retrospective analysis of patients with metastatic melanoma that showed T-VEC reduced the size of injected tumors and also non-injected
tumors that had metastasized to other parts of the body.

Of the 295 patients treated with T-VCE, almost 4,000 tumor lesions were tracked for this analysis. Half
of these lesions were injected with T-VEC at least once, while the rest were not injected, including visceral tumor lesions (tumors involving solid organs
such as the lungs and liver). The results showed a 50-percent or greater reduction in tumor size in 64 percent of injected tumors. In addition, one-third of
uninjected non-visceral tumors and 15 percent of visceral tumors were also reduced by at least 50 percent. There were 35 melanoma-related surgeries performed
during this trial, of which 30 percent successfully removed all residual disease.

The most frequently observed
adverse events in the Phase 3 study were fatigue, chills and pyrexia. The most common serious adverse events include disease progression in both groups, and
cellulitis and pyrexia in the talimogene laherparepvec group. Serious adverse events occurred in 26 percent of talimogene laherparepvec patients and 13
percent of GM-CSF patients. Immune-mediated events were reported infrequently.

T-VEC did stumble slightly by
missing on overall survival, a secondary endpoint in the Phase 3 study. However, Amgen has filed with the FDA for approval and with the European Marketing
Agency. In addition, it has started at trial in collaboration with Merck to test T-VEC in combination with Merck’s newly approved checkpoint inhibitor
Keytruda.

Allovectin-7

A less happy outcome was in
store for Vical’s Allovectin-7 (velimogene aliplasmid). For nearly two decades, velimogene aliplasmid was under investigation. It is an HLA-B7/beta2-
microglobulin plasmid formulated with cationic lipids. It increases the ability of the immune system to recognize cancer cells and kill them. In 1999, the
U.S. FDA granted Allovectin-7 orphan drug designation for intralesional treatment of invasive and metastatic melanoma. What was particularly promising was
the fact that its mechanism of action is not melanoma-specific; it has the potential to be used in other types of solid tumors.

In 2010, Vical reported encouraging results in Phase 2 trial, a single-arm, open-labeled study in which 127 chemo-refractory
or chemo-intolerant patient subjects were treated with high-dose Allovectin-7. The median age of patients enrolled in the study was 60, and patients as old
as 98 were treated with Allovectin-7, yet there were no treatment-related Grade 3 or Grade 4 adverse events, and no withdrawals from the trial for
tolerability. The overall response rate for the 127 patients receiving the high-dose treatment was 11.8 percent, with four complete responders and 11 partial
responders. The median duration of response was 13.8 months, ranging from a minimum of six months to a maximum of 66 months and still ongoing. Median
survival was 18.8 months. These data compared favorably against historical controls from other studies in metastatic melanoma. Findings from the Phase 2
trial were incorporated into the design of a Phase 3 pivotal trial through a Special Protocol Assessment agreement with the U.S. FDA.

The Phase 3 trial, initiated in January 2007, evaluated Allovectin-7 as first-line therapy in patients with Stage III or IV
recurrent metastatic melanoma. Vical completed enrollment in February 2010 of approximately 390 chemo-naive patients randomized on a 2:1 basis: approximately
260 for treatment with Allovectin-7 and approximately 130 for treatment with either dacarbazine or temozolomide.

Unfortunately for patients and the company, Vical announced on August 12, 2013, that the trial did not pan out as hoped. It failed to demonstrate a
statistically significant improvement compared to first-line chemotherapy for either the primary endpoint of objective response rate at 24 weeks or more
after randomization or the secondary endpoint of overall survival.

Rose Bengal (RB) disodium (PV-10)

Provectus Biopharmaceuticals' PV-10 is a preparation of rose bengal (a dye used by eye doctors, and
before that, in clothing) currently being investigated at both St. Luke's Cancer Center and Moffitt Cancer Center. In a Phase 2 PV-10 trial, when all
existing lesions were injected with PV-10, tumors were no longer detectable (complete response) in 50 percent of the patients (Confidence Interval: 31-69
percent). This subgroup analysis supports the potential of PV-10 as a single agent and provides a rationale for a PV-10 Phase 3 randomized controlled trial
in locally advanced melanoma patients.

In the peripheral blood of patients after PV-10 injection, researchers saw
a significant increase in circulating T-cells, including CD3+ and cytotoxic CD8+ cells. This suggests an immunologic-mediated antitumor response is
engendered by PV-10.

The study showed PV-10 elicits a high rate of response in injected tumors through its
ablative effect, and, additionally, that the durability of response as well as the bystander response in uninjected tumors implicate an additional
immunologic mechanism secondary to ablation. This appears to be similar to the experience noted in Cancer back in 1975.

Tumors were no longer detectable (complete response or CR) in 26 percent of the study population. This response was
particularly evident in patients who had all existing lesions injected with PV-10 (i.e., All Lesions Treated subgroup, 50 percent CR; Confidence Interval:
31-69 percent). These 28 patients had as many as 20 lesions confined to the skin and experienced a mean progression-free survival of 9.8 months. For an
additional 26 patients who had all their disease treated, with the exception of 1-2 designated, untreated bystander lesions, mean progression-free survival
was 8.9 months.

A separate study of PV-10 assessed response of injected and uninjected B16 melanoma tumors in mice
receiving PV-10 alone or in combination with one of three agents designed for co-inhibitory blockade. The tested agents targeted either CLTA-4, PD-1 or PD-
L1, the three most common clinical targets for co-inhibitory blockade. In each case, combination of PV-10 with co-inhibitory blockade led to improved tumor
response and enhanced anti-tumor immunity of T-cells. Further testing with the anti-PD-L1 agent showed that these improvements could apply to both injected
and uninjected tumors.

Based on the findings from St. Luke's and from Moffitt, Provectus has submitted a Phase
3 protocol to the FDA for a Phase 3 randomized controlled trial of PV-10 in patients with unresectable locally advanced cutaneous melanoma that will assess
response to PV-10 versus that of systemic chemotherapy in patients who have disease limited to cutaneous and subcutaneous sites and who have failed or are
ineligible for systemic immunotherapy. In addition, Provectus is investigating the efficacy of PV-10 for other indications including liver, breast and
colorectal cancers.

In Conclusion

Injecting a tumor
with a cancer-killing drug seems to make perfect sense, but as research has shown, it matters a great deal what the drug is. A generation ago, intralesional
BCG appeared to work, but when serious study of it showed problems, researchers walked away, not only from that use of the drug but also from the approach
itself. Now, intralesional treatments are making a comeback in clinical trials because the drugs being used appear to be better suited for it than BCG
was.

Peter R. Culpepper is chief financial officer and chief operating officer at Provectus Biopharmaceuticals. He has spent 20
years in the financial field working for a wide range of companies and industries in the United States and abroad, especially high-growth startups. This
commentary originally ran on our Cancer Research News website at www.ddncancer.com.